1. Field of the Invention
The invention relates to a measuring device to determine the distance between an electrically conducting part, which can be moved in a defined chamber, and a reference point, in particular to determine the upper dead point of the piston of an internal combustion engine, with an electronic evaluation circuit in which a capacitive sensor can be positioned in a holding device, held in the wall of the chamber, and is connected to an evalution circuit.
2. The Prior Art
In a known measuring device of the aforementioned kind one electrode is isolated in the combustion chamber of an internal combustion engine, the piston or the cylinder block forming the second electrode. Depending on the distance of the piston from the electrode, the capacitance of this system changes. In well-known cases, the change in capacitance is now evaluated in such a manner that said evaluation influences the modulation of a carrier frequency for which a relatively complicated evaluation circuit is necessary.
Due to this principle of measurement, the well-known system has proven to be relatively insensitive to small changes in capacitance and also exhibits a poor signal to noise ratio. In addition to this, one must work with relatively large sensors, resulting in the necessity of providing matching measurement openings, which permit the electrode to be inserted.
The object of the invention is to avoid the above drawbacks and to propose a measuring device of the aforementioned kind, which in particular can be used in a simple manner in conventional internal combustion engines and is characterized by a high degree of sensitivity.